1. Field of Invention
The present invention relates to a biological sensor which is capable of stably measuring the concentration of a gas and ions in living tissues.
2. Related Art
The measurement of the concentration of a gas, such as carbon dioxide and ammonia gas, is important in industrial applications. In recent years emphasis has come to be placed on the measurement of a gas concentration and an ion concentration in an organism in the fields of medicine and physiology. In this measurement, a very small biological sensor which can be used by being inserted in cells or a blood vessel is required.
As sensors of this type, sensors having various structures have been proposed. For example, a gas sensor disclosed in Examined Japanese Patent Publication Hei. 4-32985. FIG. 3 is a cross-sectional view illustrating the construction of one example of the gas sensor proposed therein. In FIG. 3, an ion sensor of a gate-insulated field-effect transistor structure (hereafter referred to as the ISFET) 1, a reference electrode 2, and lead wires 4 connected to electrode portions 3 of the ISFET 1 are embedded in an electrical insulating resin 6 inside a tube 5. A gate portion 7, which is an ion sensitive portion of the ISFET 1, and a portion of the reference electrode 2 are inserted in a hollow portion of a single porous hollow fiber 8, and are covered in the porous hollow fiber 8. The porous hollow fiber 8 and a space between the porous hollow fiber 8 and the ISFET 1 is filled with a space absorbing fluid 9. The porous hollow fiber 8 is further covered with a homogeneity membrane 10.
With the gas sensor constructed as described above, since the porous hollow fiber 8 is fabricated in advance by a fiber forming technology, its shape and the distribution of pores can be easily made constant. For this reason, it is possible to reduce the variations in the characteristics of the gas sensor. Further, since the porous hollow fiber 8 is not fluid and can retain a substantially fixed shape, the amount of change in the characteristics of the sensor is small. Further, by covering a distal end of the ISFET 1 with the porous hollow fiber 6, the breaking of the homogeneity membrane 10 by the distal end of the ISFET 1 can be suppressed to a certain degree.
FIG. 4 is a cross-sectional view illustrating the construction of another conventional example of this type of sensor.
This sensor is disclosed in unexamined Japanese Patent Publication Sho. 58-97346. In FIG. 4, portions corresponding to the portions of the conventional example shown in FIG. 3 are denoted by the same reference numerals, and a description thereof will be omitted, as required. The characteristic feature of this conventional example lies in that a needle 11 is provided at the distal end of the tube 5, that the ISFET 1 and the reference electrode 2 are accommodated in an opening 5a formed in side wall of the tube 5 in such a manner as to come into contact-with the gas absorbing fluid 9, and that the opening 5a is covered by the gas permeable homogeneity membrane 10. Connector pins 12 are disposed at a rear end of the tube 5, and the lead wires 4 are connected to the connector pins 12. It should be noted that reference numeral 13 denotes a reinforcing core wire embedded inside the tube 5 between its distal end portion and a connector 14.
According to the gas sensor constructed as described above, by inserting the tube 5 into living tissues through the needle 11, a state-of close contact between the ISFET 1 and the tissues is established, so that it is possible to measure the gas concentration in the tissues with excellent reproducibility.
However, according to the gas sensor disclosed in Examined Japanese Patent Publication Hei. 4-32985, since porous hollow fiber 8 is likely to be deformed by the external pressure since it has plasticity, and since the gate portion 7 of the ISFET 1 is subjected to pressure from the living tissues through the porous hollow fiber 8, the output of the sensor becomes unstable. Further, since the ISFET 1 and the reference electrode 2 are formed of rigid materials, if they are subjected to an external force, there are possibilities that these members become broken and that the gas permeable membrane 10 is punctured thereby, causing damage to the sensor structure.
On the other hand, according to the gas sensor disclosed in Unexamined Japanese Sho. 58-97346, since the tube 5 is punctured into the living tissues through the needle 11, there has been a drawback in that the living tissues can be damaged.
In addition, with the above-described two conventional examples, since no consideration is given to the fixation of the sensor to the object, there has been a problem in that the sensor is likely to come off.
Furthermore, since a shielding structure is not provided for protecting from induction noise an unillustrated leading portion for leading a signal detected by the ISFET 1 to the outside, the sensor is susceptible to the effect of such as an electric cautery, so that there has been a problem in that the signal output changes.
The invention has been devised in view of the above-described circumstances, and its object is to provide a biological sensor capable of stably measuring a gas or ion concentration in living tissues without damaging the living tissues. Another object of the invention is to provide a biological sensor which can be easily secured at a measurement region of an object.
To attain the above objects, in the invention according to first aspect of the present invention, there is provided a biological sensor including a sensor sensitive portion for detecting a gas concentration or an ion concentration in a living tissue as the sensor sensitive portion is brought into contact with the living tissue, and a leading portion for leading to an outside a signal representing the gas concentration or the ion concentration detected by the sensor sensitive portion, provided in that a protecting portion having a thickness larger than the thickness of the sensor sensitive portion surrounds the sensor sensitive portion, and is fixed to the leading portion.
Biological sensor according to second aspect of the present invention, the protecting portion is formed of a high rigidity resin or metal which is difficult to absorb a gas or ions.
Biological sensor according to third aspect of the present invention, an outer periphery of the leading portion on a sensor sensitive portion side is covered with a plasticity material.
Biological sensor according to a fourth aspect of the present invention, the plasticity material has a metal member for covering the leading portion.
Biological sensor according to a fifth aspect of the present invention, the metal member is electrically grounded.
Biological sensor according to a sixth aspect of the present invention, the protecting portion is formed of a metal, and the metal member is further electrically connected to the protecting portion.
Biological sensor according to a seventh aspect of the present invention, the protecting portion is formed of a metal, and is electrically grounded.
Biological sensor according to a eighth aspect of the present invention, the plasticity material is defined by a metal wire having plasticity and a flexible synthetic resin tube.
In biological sensor according to the first and second aspects of the present invention, since the sensor sensitive portion for detecting the concentration of a gas or ions from living tissues is surrounded by the protecting portion having a thickness larger than the thickness of the sensor sensitive portion, by placing the protecting portion between the living tissues, a signal representing the concentration of a gas or the like in the living tissues can be outputted stably without causing the living tissues to come into direct contact with the sensitive portion.
In biological sensor according to the third and fourth aspects of the present invention, since the outer periphery of the leading portion is covered with the plasticity material, the leading portion can be fixed stably by being curved at an angle conforming to a measurement region.
In biological sensor according to fourth to seventh aspects, since the metallic protecting portion and the metal member are electrically grounded, it is possible to reduce induction noise due to high frequencies from an electric cautery or the like to which the leading portion is subjected, thereby making it possible to obtain a stable signal output. Namely, since the induction noise caused by electric cautery is likely to affect the sensor signal through the leading portion, the grounding of the metal member of the plasticity material produces a large effect. In cases where the plasticity material does not include a metal member, it is possible to enhance the effect by leading the grounding line of the protecting portion together with the tube. Further, in order to obtain an enhanced effect, it is preferable to include a metal member in the plasticity material and ground both the metallic protecting portion and the plasticity material.
In biological sensor according to the eighth aspect of the present invention, by covering the metal wire having plasticity with the flexible synthetic resin tube, it is possible to prevent the danger of elution of metal ions and leakage current into the living tissue and the like.
In biological sensor according to a ninth aspect of the present invention, the protecting portion prevents an excess pressure from being applied to the sensor sensitive portion when the biological sensor is disposed in the organism, and the protecting portion causing the gas to diffuse toward the sensor sensitive portion from at least two directions.